Then I upgraded the system and after restarting this error appeared....

Slackel.example.net: Starting up X11 manager...
/usr/sbin/gdm-binary: /lib64/libm.so.6 version 'GLIBC_2.29' not found (required by /usr/lib64/libEGL.so.1)
/usr/sbin/gdm-binary: /lib64/libm.so.6 version 'GLIBC_2.29' not found (required by /usr/lib64/libGL.so.1)
/usr/sbin/gdm-binary: /lib64/libm.so.6 version 'GLIBC_2.29' not found (required by /usr/lib64/libgbm.so.1)